This invention relates to a printed wiring board which is available as a relay board that relays electric signals.
For example, this type of printed wiring board is disclosed in JP-A 2012-64338 (Patent Document 1), the content of which is incorporated herein by reference.
As shown in FIGS. 13 and 14, a board (printed wiring board) 900 disclosed in Patent Document 1 is formed with electrodes (signal electrodes) 910, ground electrodes 920 and grounded plates 930. The ground electrodes 920 are connected with the grounded plates 930, respectively. The board 900 is connected with twinaxial cables (cables) 940 and has shield covers 950 attached thereto. Each of the cables 940 has a conductive line (signal conductor) 942, a dielectric body 944 covering the signal conductor 942, a shield layer (ground conductor) 946 covering the dielectric body 944, and a drain wire 948 connected to the ground conductor 946. The dielectric body 944 and the ground conductor 946 are peeled off at an end portion of the cable 940 to expose the signal conductor 942. The signal conductor 942 is connected to the signal electrode 910 of the board 900 while the ground conductor 946 is connected to the ground electrode 920. The drain wire 948 is connected to the shield cover 950.
The shield cover 950, the ground electrode 920 and the grounded plate 930 are connected together and cover around the end portion of the cable 940, or around the exposed portion where the dielectric body 944 and the ground conductor 946 are peeled off. Because the exposed portion of the cable 940 is thus covered by the ground potential, impedance of the exposed portion of the cable 940 can be matched with impedance of an unexposed portion that is other than the exposed portion.
The board 900 of Patent Document 1 is required to have the shield cover 950 attached thereto, wherein the shield cover 950 is formed separately from the board 900. Accordingly, material cost and assembly cost increase. Moreover, because this structure makes it difficult for the pitch of the signal electrodes 910 to be smaller, the board 900 is difficult to be reduced in size. In addition, the board 900 and the shield cover 950 have a gap formed therebetween, wherein the gap has a size nearly equal to a thickness of the signal electrode 910 or the ground electrode 920. Accordingly, for example, when two cables 940 are connected to adjacent two of the signal electrodes 910, respectively, these adjacent signal electrodes 910 might cause cross-talk therebetween along a surface of the board 900.